New Geometric Average Method for Calculation of Ultimate Bearing Capacity of Shallow Foundations on Stratified Sands

Obtaining the bearing capacity of shallow foundations in a nonhomogeneous soil profile has been a challenging task in geotechnical engineering. In this paper, a new geometric average for the equivalent soil friction angle (phi) of various layers beneath shallow strip foundations is used to determine the ultimate bearing capacity. This approach is based on the concept of geometric mean value; however, the method involves applying a power to each variable, which is here the internal friction angle of each soil layer. Numerical methods based on finite elements and also experimental data have been used to verify the presented average method. It will be shown that data obtained from the developed method are well in agreement with those obtained from finite-element analysis and with those obtained from full-scale loading. This agreement is closer when the difference between the shear strength parameters of layers is small, which is the case for sedimentary soil profiles and also for artificially compacted soils. A computer program has been developed to investigate the influence of various parameters and to compute equivalent f for different cases. (C) 2013 American Society of Civil Engineers.